{Mjagkova_Jana 20.09 2S}
program ploshad2S;

{$APPTYPE CONSOLE}

uses
  SysUtils;

var
x1,y1,x2,y2,x3,y3,S: Integer;
begin
  readln(x1,y1,x2,y2,x3,y3);
  S:= (abs( x1*y2-x2*y1+y3*x2-x3*y2+x3*y1-x1*y3)) div 2;
  Writeln(S);
  Readln;
end.
